Ok, I know HTML is not the most important thing on the site, but that kind of thoughts only leads to procrastination, because there will always be issues on other stuffs like databases and security, but it would be nice to HN pays a little of atention to this kind of stuff.
Who cares if the html is crufty as long as it works. I use table layouts quite often, and if you look at the source of stackoverflow they use tables too.
What I would like to see are a few functionality tweaks to make HN more useful. The main ones that come to mind are: increasing the timeout before you get an 'unknown or expired link' and optionally emailing you when someone replies to one of your comments.